Various types of user input devices may provide position signals to a computing device. For example, eye tracking systems may be used to track a location at which a user's gaze intersects a displayed user interface. Various mechanisms may be used to track eye motions. For example, some eye tracking systems may include one or more light sources configured to direct light (such as infrared light) toward a user's eye, and one or more image sensors configured to capture images of the user's eye. Images of the eye acquired while the light sources are emitting light may be used to detect the location of the user's pupil and of corneal (or other) reflections arising from the light sources. This information may then be used to determine a position of the user's eye. Information regarding the user's eye position then may be used in combination with information regarding a relative location of the user's eye compared to the user interface to determine a location at which the user's gaze intersects the user interface, and thus to determine the position signal.